Our long-term objective is to characterize the physiological processes that underlie involuntary muscle contractions, weakness and fatigability, major problems encountered in skeletal muscles paralyzed by injury or disease. In individuals with skeletal muscles paralyzed (not under voluntary control) by spinal cord injury, our Specific Aims are: 1) to quantify involuntary activity (spasms) from surface electromyographic signals (EMG) recorded from 8 leg, arm and hand muscles over 24 hours. EMG data from spinal cord injured people who take no medication to control spasms (non-users) will be compared to their activity log and to voluntary EMG recorded from able-bodied subjects. Whole muscle contractile properties will be measured to assess whether these involuntary contractions counter the effects of muscle disuse. Repeat experiments will be used to establish the validity of the 24-hr EMG recording technique;2) to evaluate whether single interventions (exercise, baclofen) and combined interventions (exercise and baclofen) alter the number, duration and intensity of spasms. 24-hr EMG recordings will be made in non-users and chronic baclofen users who stop this drug. Analysis of spasms before and after each intervention will show the acute extent (within 24 hrs) to which exercise (baclofen;exercise and baclofen) changes spasms in the same subject. Comparison of spasms across experiments involving different interventions will reveal the effectiveness of exercise versus baclofen or the combined intervention as a treatment to reduce involuntary muscle contractions;3) to examine whether exercise (baclofen, exercise and baclofen) alters muscle spasms by changing inhibitory processes, motoneuron excitability, and/or muscle responses. Quantifying spasms during natural unconstrained behaviors over an entire day will improve our understanding of muscle spasms, the most debilitating aspect of the spasticity that is so prevalent after spinal cord injury and other neuromuscular disorders. These studies will also determine the effectiveness of therapies used to control involuntary muscle activity after spinal cord injury. If muscle spasms prevent deterioration, the widespread use of medication should be re-evaluated. PUBLIC HEALTH RELEVANCE. Muscle spasms often interfere with care and mobility after spinal cord injury. Documenting muscle activity over 24 hours in relation to the activity log of the person with spinal cord injury will show what features of these contractions disrupt daily activities. Analysis of whether exercise and/or anti-spasm medication reduces involuntary contractions will clarify whether the treatments currently used to control unwanted muscle contractions need revision.